I think you're describing a bent front wheel, but I can't tell for sure. But a bent wheel won't cause the bar to pull to one side while riding. That's caused by misalignment of parts that support the wheel. If parts are needed, there are sources like partzilla.com, and you can check prices there.
You can get a petcock rebuild kit, or talk to Ducatiman, who rebuilds them reasonably.
Put a voltmeter's probes directly on the battery terminals while cranking or trying to crank, and read the voltage. That will tell you if the battery is the problem.
The clutch is adjusted externally. You need a copy of the shop manual. In the meantime, the How-To pages should help.
https://faq.ninja250.org/wiki/Ninja250_Howto